Todd, I am attaching a copy of my TC35/40/45 hydraulic system because surely it is a similar New Holland design.
You are getting so many ideas that I am afraid you are being sent on a "wild goose chase" and wasting time instead of isolating your problem. I know your 1920 is different from my TC45, but I bet it is not that different, so I am attaching a scan of the hydraulic system from my repair manual so we have some definite commonality in nomenclature in our discussion of your problems. The illustration is 720 x 950, so you might want to print it out so you can look at it while you read the rest of my post (very long and windy)./w3tcompact/icons/laugh.gif
I have my opinion, and I'm sure others will have good suggestions too, so here goes:
The pump (item 4) draws fluid from the reservoir (item 1) and supplies pressure to the system diverter and relief valve. If you did not have a FEL, this valve would be rotated open so the fluid would go directly to your 3PH and Backhoe, but note that ALL fluid is diverted through the FEL control valve before going to the 3PH system. If the relief valve in this diverter was stuck open, your FEL would not work, so I am going to suggest you eliminate that as a possible problem.
Continuing on to the remote valve (item 8), there could be a problem here, but this is where your tractor is going to be different because of your backhoe, but notice that in my diagram, ALL fluid flows thru this valve and the endcap (item 10) before it gets to the 3PH HPL valve (item 11). If there is a leak in any of these items, you could be losing pressure here. Following the pressure source to the 3PH HPL valve (item 11), notice that it has internal pressure relief and dump valves (unloading valves) that return to the reservoir (arrows to the right). Pressure is then supplied to the flow valve (item 12) which also has a check/relief valve at the top of the diagram. I don't think the flow valve is your problem either. Here is my thought process...
1. Your pump is working, but fluid is not leaking out of the tractor, so it must be getting back to the reservoir through a normal path or an internal leak.
2. If it is getting back to the reservoir thru a normal path,
my diagram shows one of four ways it can go.
a. from the system relief diverter valve (item 5)
b. from a remote control valve (item 8, your backhoe
is probably attached in a similar position)
c. from the system hydraulic lift HPL (control) valve
(item 11, the control valve for your hydraulic lift)
d. from a relief valve in your flow control valve (item 12)
3. If it was anything after the backhoe, your backhoe would work because of the design of the system. Because the leak is in the connection to the backhoe, nothing in the system after the backhoe works (i.e. the 3PH). Because you can get minimum pressure to the the 3PH and backhoe if you rev the rpm's up to 2500, this just means that you have a leak that is not dropping 100% of the pressure. When you open the lines and see flow, I bet you could almost stop it by putting your thumb over the hole (although I recommend using something beside your thumb to test this theory). If you could loop the supply to your backhoe to the return (effectively eliminate the external backhoe) you could then prove the leak is internal to the tractor. I'd look at removing all external endcaps and backhoe interface and look for a stuck relief valve or blown seals in these assemblies before removing your entire 3PH assembly.
Good luck. I hope this is help instead of leading you down the wrong path./w3tcompact/icons/crazy.gif
